1. Field of the Invention
The present invention relates to a color sorting apparatus for granules, and more particularly to a color sorting apparatus equipped with a display control device that is configured to be able to sense images of a granule picked up by a CCD sensor to thereby display the images on an operation panel and perform detection sensibility control for the defective granules while observing the displayed images.
2. Description of the Related Art
When performing the control of the background or sensibility in the conventional color sorting apparatus, sensor signals were displayed on an oscilloscope or a touch panel to carry out the control while observing the displayed signals. More particularly, in the conventional sensibility control of thinly-coloration and partly-coloration for the defective granules such as thinly-colored granules and partly-colored granules, the falling level of signals to be regarded as the defective granule has been carried out based on the magnitude of the falling with respect to the background signal level being set to 100% while observing the actual sorting condition. The key map of the conventional sensibility control is shown in FIG. 6. In this figure, it is shown that a granule whose sensed level being fallen to 75% or less with respect to the background signal level being set to 100% is determined as the thinly-colored defective granule, and a granule whose sensed level being fallen to 50% or less with respect to the same is determined as the partly-colored defective granule.
The above explained conventional background control and sensibility control greatly depend on human senses and experiences since such controls are carried out while observing the actual sorting condition, and the matters of how a CCD sensor actually senses the granule and on what basis the signal processing section detects a granule as a defective granule had been estimated on the basis of the results of the actual sorting, without clarifying such matters.
However, when such controls are made only based on the actual sorting results, there have been cases in which the background control and the sensibility control do not always accurately associate with the sorting results, since the sorting results are also influenced by other factors including the performance, timing control and the like of an ejector which is arranged at the downstream side of a sensing means for the defective granules.
Another conventional technique is disclosed in Japanese Patent Application Kokai-Publication No. 11-94749. In this disclosure, there is disclosed a technique wherein the frequency distribution of quantity of light of the respective light received data is displayed on an operation panel of a color sorting apparatus and an operator can set up an appropriate range of quantity of light (i.e., a difference between the upper limit threshold and the lower limit threshold) while observing the display. However, the technique of this disclosure also is directed to determine whether the control or setting of the threshold is appropriately carried out or not from the actual sorting results. Hence, this technique is not different from the foresaid prior art in terms of that the control is dependent on senses and experiences of the operator.
As described above, in either of the above-explained prior arts, the determination whether the respective thresholds in order to sense the defective granules are in the state being properly set up or not has been made by observing the actually-sorted defective granules. Further, based on the sorting results, the controls of the respective thresholds were repeatedly executed by necessity until the sorting results have come to be the proper sorting results in view of human senses and experiences.